ORIGIN OF EXCITED MERCURY - AMMONIA EMISSION AT LOW-PRESSURES - REPLY

Umemoto et al. have recently published a mechanism for the Hg(3P1) photosensitisation of NH3, proposing that the short wavelength component of the luminescence arises directly from a reaction of Hg(3P1) with NH3: Hg(3P1) + NH3 → HgNH†3, HgNH†3 → Hg + NH3 + hv (short λ). From a detailed analysis of the kinetics, Callear and Freeman had previously concluded that the carrier is an excited complex formed in a bimolecular reaction of Hg (3P0) and NH3. To reveal the identity of the essential precursor, we have monitored the intensity of the short wavelength spectrum in experiments in which the relative concentrations of Hg(3P1) and Hg(3P0) were widely varied. All the results are in excellent accord with the mechanism of Callear and Freeman. Particularly striking is the effect of adding N2 to small pressures of NH3, which can increase the intensity by two orders of magnitude without significantly changing the Hg(3P1) concentration. From time resolved measurements we also conclude that any emission arising directly from reactions of Hg(3P1) is negligible. In the course of this research we have discovered that CO efficiently deactivates the stabilised NgNH3 (A2). The rate of coefficient is 2.0 (± 0.1) × 10-10 cm3 molecule-1 s-1. © 1978.